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December Weather in Cornwall, United States

Last updated: June 24, 2025

In Cornwall, United States, the average temperature in December hovers around 1°C (35°F), with a minimum of -17°C (2°F) and a maximum of 17°C (62°F). Expect 102 mm (4.0 in) of precipitation spread across 11 days, and enjoy a relatively high average humidity of 80% during this chilly month.

December Temperature in Cornwall

In December in Cornwall, the average temperature is 1°C (35°F). Maximum temperatures can reach 17°C (62°F), while minimums can drop as low as -17°C (2°F). Be prepared for a wide range of temperatures when traveling to Cornwall during this month.

December Weather in Cornwall: Daily Temperature Highs, Lows, and Averages

The chart illustrates December temperature patterns in Cornwall, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Cornwall, December typically has an average temperature of 1°C (35°F), with highs reaching up to 17°C (62°F) and lows dropping to around -17°C (2°F).
JanFebMarAprMayJunJulAugSepOctNovDec303339496069757366564234
Data source: Temperature data for Cornwall generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

December Precipitation in Cornwall

In Cornwall in December, the precipitation amount is 102 mm (4.0 in) over the course of 11 days.

December Precipitation Trends in Cornwall

The chart displays monthly precipitation patterns in Cornwall, with values for each month alongside December’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how December’s conditions compare to those of other months. In Cornwall, December typically receives around 102 mm (4.0 inches) of precipitation spread over approximately 11 days.
JanFebMarAprMayJunJulAugSepOctNovDec6995881181199512912111514190102
Data source: Precipitation data for December generated using information from the Copernicus Climate Change Service.
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December Humidity in Cornwall

In Cornwall in December, humidity is 80%. With an average temperature of 1°C (35°F), this humidity feels like a cold, damp embrace that makes traveling quite uncomfortable, as it seeps into your clothes and makes the air feel heavier, making it hard to stay warm and dry while exploring.

December Average Humidity in Cornwall

This chart illustrates the average monthly humidity levels in Cornwall, with December’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In December, average humidity in Cornwall is approximately 80%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec84%82%81%78%70%69%62%65%68%74%82%80%
Data source: Humidity data for December generated using information from the Copernicus Climate Change Service.

December UV Index in Cornwall

In Cornwall in December, the maximum UV index is 2, which corresponds to a low exposure category. With this level of UV radiation, the time to burn is approximately 45 minutes. To learn more about the hourly UV index in Cornwall, you can visit Hourly UV Index in Cornwall.

Maximum UV Index Levels in Cornwall for December

The chart shows the monthly maximum UV Index (UVI) for Cornwall in December, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In December, the maximum UV index in Cornwall typically reaches 2, which falls under the low exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec356810101098642
Data source: Cornwall December UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

How December Weather in Cornwall Compares to Other Months

Weather in Cornwall varies notably across the year, with each month offering distinct climate conditions. This page compares December’s weather to other months in Cornwall, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in Cornwall, showing how December’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-1°C (31°F)69 mm (2.7 inches)84%moderate
February Weather1°C (33°F)95 mm (3.7 inches)82%moderate
March Weather4°C (39°F)88 mm (3.5 inches)81%high
April Weather10°C (50°F)118 mm (4.6 inches)78%very high
May Weather15°C (60°F)119 mm (4.7 inches)69%very high
June Weather20°C (69°F)95 mm (3.7 inches)69%very high
July Weather24°C (75°F)129 mm (5.1 inches)62%very high
August Weather23°C (73°F)121 mm (4.8 inches)65%very high
September Weather19°C (67°F)115 mm (4.5 inches)68%very high
October Weather14°C (57°F)141 mm (5.5 inches)74%high
November Weather6°C (42°F)90 mm (3.5 inches)82%moderate
December Weather1°C (35°F)102 mm (4.0 inches)80%low

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